Fluid conditioning apparatus and system

ABSTRACT

A system for conditioning working fluid in environmental control systems includes arrangements for minimizing icing from a variable flow velocity turbine exit flow at subfreezing conditions wherein the turbine is very closely located to the downstream heat exchanger, including a backpressure plate for minimizing flow velocity stratification, an internal bypass passage arranged to produce a relatively predictable bypass flow ratio regardless of the flow velocity stratification, and other anti-icing techniques.

The United States Government has rights in this invention in accord withthe provision of Contract No. N00019-85-C-0145 with the United StatesNavy.

CROSS-REFERENCE TO RELATED APPLICATION

Subject matter common to that disclosed herein is also contained incommonly assigned U.S. patent application Ser. No. 482,150 filedsimultaneously herewith and entitled "Fluid Conditioning Apparatus AndSystem".

BACKGROUND OF THE INVENTION

1. Field Of The Invention

This invention pertains to the art of fluid conditioning apparatus,systems and methods, and is more particularly concerned withimprovements for preventing excessive ice formation at the cold fluidinlet of heat exchangers in these systems, as well as for providingimproved heating capacity utilizing the heat transfer performancecapabilities of heat exchangers. These apparatus are most commonly used,but are not limited to, environmental control systems for air and groundvehicles, both military and commercial.

2. Description Of Prior Art

Examples of arrangements for preventing excessive ice formation aredescribed in three patents. The first is U.S. Pat. No. 4,198,830 datedApr. 20, 1980, of Carl D. Campbell, and entitled "Fluid ConditioningSystem And Apparatus". The second is U.S. Pat. No. 4,246,963 dated Jan.27, 1981, of Alexander Anderson, and entitled "Heat Exchanger". Thethird is U.S. Pat. No. 4,352,273 dated Oct. 5, 1982, of Robert C.Kinsell et al, and entitled "Fluid Conditioning Apparatus And System".All of the above patents are assigned to the same assignee as that ofthe present invention.

Briefly stated, the Campbell invention provides a means to condensewater out of the working fluid of an air-cycle environmental controlsystem while the fluid (air) was still at high pressure, eliminating theneed for coalescer bags which require significant maintenance. A problemwith ice formation on the face of the heat exchanger in line with thedischarge of the expansion turbine was addressed by the Andersoninvention which proposed the addition of hot header bars, not connectedto the cold passages, for improved ice prevention characteristics of theheat exchanger. The Anderson invention also detailed the heat transferrelationship between the hot and the cold side fins necessary tomaintain metal temperatures above freezing. The Kinsell et al inventionprovides for the substantial lowering of the expansion turbine dischargeair temperature and an associated increase in the delivered coolingcapacity of a typical apparatus by adding a bypass in the middle of theheat exchanger.

In addition to the type of air cycle environmental control system (ECS)described in those patents, the present invention is useful in an ECSsystem variation wherein condensing heat exchanger is used to achieveextra heating capacity in a combined ECS, nuclear-biological contaminantfiltration system while maintaining the proper environmental conditionsat the filter inlet. This cycle also relies on the three previouslydescribed patents for the prevention of ice in subfreezing condensers.The above inventions have found successful application in bothcommercial and military air and ground vehicle environmental controlsystems. However, the methods described above for controlling theformation of ice have normally required additional, active methods ofice control.

Applications of the Anderson invention have shown that the performanceof the condenser heat exchanger changes dramatically with changes inoperating conditions, specifically turbine discharge velocities. This isdue to the design of the heat exchanger cores described in the Andersoninvention. The variation in performance is due to the very low pressureloss of the condenser core relative to the manifold pressure losses. Inother heat exchangers, core pressure losses are typically 80% of theflange-to-flange pressure loss to ensure proper flow distributionthrough the heat exchanger. The Anderson invention provides for veryloose fins on the cold side passage of the heat exchanger to prevent theaccumulation of ice by reducing the blockage of the flow path and bybiasing the metal temperatures closer to the hot side than the coldside. The resulting design is therefore very sensitive to flowstratification at the condenser cold side inlet.

Testing of various systems utilizing the referenced inventions has shownthat, when the turbine is close-coupled to the condenser, as it is inmost systems, changes in turbine exit velocity produce significantchanges in the flow and temperature stratification of the condenser coldside inlet.

SUMMARY OF THE INVENTION

An important aspect of the present invention is a postulation that thisabove-described stratification produces significant deviations frompredictions of metal temperatures for these prior arrangements. Theconcentration of cold air from the turbine exhaust in the center of thecondenser core results in lower than predicted metal temperatureslocally, and the formation of ice when no ice is predicted. This isbelieved to be a primary reason for use of secondary, active de-icingdevices in these systems. Additionally, the amount of heat transferproduced by the heat exchanger varies significantly from predictions inwhich stratification are not accounted for, resulting in oversizedcondensers to meet water removal or heating requirements. Also, there isa problem with the predictability of heat exchanger performance inoff-design conditions where turbine exit velocities vary significantlyfrom design cases.

With these problems in mind, the present invention is intended toeliminate the variation in condenser heat transfer performance whileretaining the benefits of the Anderson invention for ice protection.This will allow the Campbell, Anderson and Limberg inventions tofunction properly in typical aircraft installations where the condenserheat exchanger of an air-cycle system is close-coupled to the expansionturbine. This will also allow repeatability and predictability inperformance predictions in off-design conditions.

More particularly, the present invention recognizes that the condenserheat exchanger described above, in order to perform consistently andavoid excessive ice formation in conditions of inlet stratificationexperienced when close-coupled to the turbine exit, must be designed insuch a manner that the inlet air is properly distributed to the coldside inlet of the heat exchanger.

The apparatus and method of the present invention for distributing theinlet flow, comprises a backpressure plate attached to the back of thecondenser heat exchanger core, which is offset from the core to allowflow through all passages. The design of this plate is such that theoverall pressure loss of the condenser is higher than without the plate,allowing the retention of the hot and cold fin heat transferrelationship described in the Anderson invention. By placing the plateon the back side of the core, the turbine exit air has been reheated inthe condenser heat exchanger and therefore the plate will not collectice. The resultant effective flow area of the core is less than theinlet manifolds, and this results in a more normal relationship betweencore and manifold pressure losses.

Another important aspect of the present invention is the recognitionthat such flow stratification may have a significant impact in theoperational aspects of an integral bypass duct or gap configuration astaught in the Kinsell et al patent. Testing with the Limberg inventionhas shown that, when the turbine is close-coupled to the condenser, asit is in most systems, changes in turbine exit velocity producesignificant changes in the flow and temperature stratification of thecondenser cold side inlet. This stratification produces significantvariation in the percentage of flow passing through the gap.

With this problem in mind, this invention is intended to eliminate thevariation in condenser bypass ratio while retaining the benefits of theKinsell invention for ice protection. This will allow function properand allow functioning, repeatability, and predictablity in performancepredictions in the systems. More specifically, the invention recognizesthat the condenser gap described above, in order to perform consistentlyin conditions of inlet stratification experienced when close-coupled tothe turbine exit must be placed in such a manner that the gap is outsideof the turbine exit high velocity area, so that changes in the turbineexit velocity will have minimal impact on the designed condenser bypassratio. Testing has shown that an internal location of the gap on theextreme side of the condenser, rather than in the middle, accomplishesthis purpose. In order to keep the outside wall of the gap fromfreezing, a small, one-pass heat exchanger is required to keep the metaltemperatures sufficiently warm.

Another aspect of the present invention is improved bypass duct capacitywhile avoiding icing therein. Specifically, inclusion of a closure plateover a part of the bypass duct, near its exit, but in a manner avoidingreduction in size of the smallest dimension of the duct, allows lowerbypass ratios without increasing ice formation. Additionally, thepresent invention contemplates anti-icing by the convenient utilizationof hot, waste fluid flow from the system, such as exhaust flow fromfluid film foil bearings.

These and other objects and advantages of the present invention arespecifically set forth in, or will become apparent from the followingdetailed description of the preferred arrangement, when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a fluid conditioning systemembodying the principles of the present invention;

FIG. 2 is a partial, cross-sectional elevational view of the air cyclemachine 20;

FIG. 3 is a partially schematic, partial front elevational view of thecondenser heat exchanger 14;

FIG. 4 is a right side elevational view, taken along lines 4--4 of FIG.3;

FIG. 5 is an enlarged cross-sectional, front elevational view of thecore portion of heat exchanger 14 with the fluid plenum casings thereofnot shown, as viewed generally along lines 5--5 of FIG. 6;

FIG. 6 is a right side elevational view of the outlet portion of theheat exchanger core as viewed along line 6--6 of FIG. 5;

FIG. 7 is a left side elevational view of the inlet portion of the heatexchanger core as viewed along line 7--7 of FIG. 5; and

FIG. 8 is a schematic depiction of flow through bypass duct 254.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

One form of the apparatus of the invention, and one form of the systememploying the apparatus, is illustrated on FIG. 1 wherein the system 10for the conditioning of the air supplied from a source to an inlet 11, apoint of use as, for example, the cabin of the aircraft, through anoutlet 13, employs an apparatus 12 comprised of a first heat exchangemeans 14, a second heat exchange means 16, a water trap or separator 18and an air cycle machine 20. The machine 20 is of the three-wheel typegenerally known in the art, comprising an air expansion turbine 22 and acentrifugal type air compressor 24 with the turbine and the compressorwheels mounted on a common rotatable shaft, together with a fan wheel.The air cycle machine structure is described in greater detail belowwith respect to FIG. 2.

The heat exchange means 14 in its preferred form is of the typefamiliarly known in the art as a counterflow plate-fin device having finmeans (not shown on FIG. 1) defining a first fluid passageway meansseparated by plate means (also not shown on FIG. 1) from a secondpassageway means defined by counterflow-disposed fins (also not shown).Fluid flowing from a chamber defined by the plenum casing 26 through thefirst passageway means enters a chamber defined by a plenum casing 28after having been in heat exchange relationship with fluid flowingthrough the second passageway means from a chamber defined by the plenumcasing 30 and entering a chamber formed by the plenum casing 32. Thecounterflow plate-fin-device 14 is described in greater detailhereinbelow with respect to FIGS. 3-8.

The heat exchange means 16 is similar to the heat exchange means 14,having similar means forming third and fourth passageway means forfluids in heat exchange relationship, with the exception that heatexchange means 16 is of the type commonly referred to as a cross-flowheat exchanger. Fluid flowing from a chamber defined by the plenumcasing 34 through the third passageway means enters a chamber defined bythe plenum casing 36. Similarly, fluid flowing from a chamber defined bythe plenum casing 38 through the fourth passageway means enters achamber defined by the plenum casing 40.

A third heat exchange means 42 commonly designated as a secondary heatexchanger which is also preferably of the cross-flow plate-fin typedefines a fifth passageway means for the flow of fluid from a chamberdefined by the plenum casing 44 through the fifth passsageway means tothe chamber defined by the plenum casing 46. The flow path over thefifth passageway means defines a sixth passageway means of the heatexchange means 42.

A fourth heat exchange means 48, commonly designated as a primary heatexchanger, which is likewise of the cross-flow plate-fin type, defines aseventh passageway means for the flow of fluid from a chamber defined bythe plenum casing 50 through the seventh passageway means to the chamberdefined by the plenum casing 52. The flow path through the seventhpassageway means defines an eighth passageway means of the heat exchangemeans 48.

A duct 54 defines a passageway for coolant fluid admitted at the upperend 56 and discharged at the lower end 58 thereof. As used in aircraft,the duct 54 would be disposed to conduct coolant ram air from ambientthrough the sixth and eighth passageways of the heat exchange means 42and 48.

Forced flow of the ambient coolant air flow through the duct 54 when theram effect is insufficient (as, for example, with the aircraftstationary on the ground) is achieved, for example, fan wheel 70disposed on the outboard end of the output power shaft of the air cyclemachine 20, fan 70 serves to pump the air from the inlet end 56 throughthe outlet end 58 of the duct 54 in known fashion, causing cooling airto flow through the said sixth and eighth passageways of the heatexchange means 42 and 48, respectively, in heat exchange relationship tothe hotter working fluid in the said fifth and seventh passageways.

To enhance the cooling effect of the cooling air flowing through theduct 54, water evaporation means therein may be employed. To this endthere is provided a water conducting pipe 51 whose inlet is coupled tothe trap 18 to conduct water therefrom to a supply nozzle 53 disposed inthe duct 54 upstream from the cooling passes of the heat exchanger means42 and 48.

Working fluid from the exterior source (and which may be initiallypressurized thereat) is caused to enter the system 10 through an inletduct 74, through plenum casing 50, and thence into the seventhpassageway means of the fourth heat exchange means 48, and thereafterthrough a duct 76 to the inlet of the compressor 24. From the exhaust ofthe compressor, the air, which has been compressed and heated even moretherein, is conducted by a duct 78 to the fifth passageway means of theheat exchange means 42 and thence through plenum casing 46 and duct 80to heat exchange means 16.

For temperature regulation, a bypass passage 60 extends from duct 74 toduct 76 in parallel to the primary heat exchanger 48, and mixing valves62,64 may be variably adjusted to control the relative airflow ratesthrough the two parallel paths and thereby adjust temperature of airflowreaching compressor 24. Similarly, a bypass passage 66 extends from duct78 to duct 80 in parallel to the secondary heat exchanger 42, and mixingvalves 68,72 may be variably adjusted to control the relative airflowrates through these two parallel paths to control the temperature ofairflow reaching plenum casing 38. As shown, a single actuator 71 may beused to simultaneously further open one and close the other of valves68,72.

It will be seen that the source working air which reaches this point ofthe plenum casing 38 of the heat exchange means 16 has been cooled inthe heat exchange means 48, heated by the compressor 24 and then cooledin the heat exchange means 42, substantially to the extent of the amountof the heat of compression imparted thereto by the compressor 24. Theheat exchange means 16 may also be designated as a reheater means sincethe pressurized hot source air entering the fourth passageway meansthereof gives up heat to the fluid flowing through the third passagewaymeans thereof. The cooled high pressure air is thereafter conducted by aduct 82 to the inlet of the plenum casing 30 and thence into the secondpassageway means of the first heat exchange means 14 wherein furthercooling occurs by the fluid flowing in the first passageway meansthereof. At this point a condensation of the water (entrained in vaporform in the source air) occurs. Thus, the first heat exchange means 14also may be designated as a condenser means.

The cooled air and entrained water droplets and mist then flow through aduct 83 from the condenser means 14 to the water trap or separator 18wherein substantially or nearly all of the condensed water is removed,with the relatively dry air then flowing through a duct 84 to the inletof the plenum casing 34 and thence into the third passageway means ofthe reheater means 16 where it is again heated by the hot source fluidin the fourth passageway thereof, as aforesaid. A parallel bypasspassage 85 extends from duct 84 in non-heat exchange, non-heatedrelationship to reheater 16, to control the temperature of airflowdelivered to downstream duct 86. As before with respect to bypasses 60and 66, a pair of valves 87,89 variably control airflow to plenum casing34 and bypass 85 (as by a single actuator as illustrated if desired) fortemperature control.

Interposed in duct 86 is a filter means 91 for extraction of certaincontaminants from the airflow prior to its introduction into habitableairspace. An example of such a filter would be a charcoal type filterfor absorption of biological or nuclear contaminants. Such type filtershave a life and efficiency highly sensitive to temperature and humidity,requiring in the environmental control system of the type illustrated inFIG. 1, that the filter be located downstream of reheater 16. Even so,in certain operating conditions the temperature of airflow exitingplenum 36 of the reheater could become excessive, requiring use ofbypass 85 to limit temperature of airflow in duct 86. Additional effectsof the necessarily limited temperature environs for filter 91 arediscussed in greater detail below.

Upon exiting filter 91, a small portion of the airflow may be divertedfrom duct 86 to a secondary outlet 93. As well known to those skilled inthe art, outlet 93 may extend to an oxygen-nitrogen generator (notshown) which operates through reverse osmosis processes to createoxygen-enriched and nitrogen-enriched airflows for other uses within theaircraft environment.

From filter 91 the relatively hot airflow passes to the inlet of theexpansion turbine 22 where it is expanded and cooled to a pointconsistent with the energy imparted by the turbine 22 to the compressor24 and the fan wheel 70. As will be apparent to those skilled in theart, the turbine and compressor operate in what is familiarly known asboot strap fashion.

From the outlet of the turbine 22 the cooled air is conducted by a duct88 to the plenum casing 26 of the condenser 14 wherein the air flowsthrough the said first passageway means to the chamber within the plenumcasing 28 and into a duct 90 to thereafter be conducted to the point ofusage as, for example, the cabin air distribution system of theaforesaid passenger aircraft. Cold air in the first passageway meansextracts such heat from the working fluid in the second passageway meansas may be necessary to effect the condensation of water in the secondpassageway means as aforesaid.

In accord with U.S. Pat. No. 4,246,963, condenser 14 is of the typehaving hollowed, heated header bars traversing the cold air inletadjacent plenum 26. A duct 92 therefore extends from duct 80 to theseheader bars (not shown in FIG. 1) to pass a portion of hot airtherethrough to assist in preventing excessive ice formation. As known,the de-icing flow from duct 92 and the header bars is discharged intoplenum 32 to mix with the cooler air therein flown from the secondpasssageway means.

The system illustrated in FIG. 1 is of the type wherein all airflow topass into the habitable space from outlet 13 is routed through theabove-described flow path in FIG. 1. Thus, for example, all airflow isthereby treated by filter 91. Heat exchanger 14 is therefore necessarilysized to accomplish two purposes: condensation of the moisture in thehot airflow passing from plenum casing 30 to plenum casing 32 asdiscussed above; and also to accomplish significant heating of thesubfreezing airflow that enters plenum casing 26 so as to produce thedesired temperature at outlet 13. This heating function requires asubstantially greater size (e.g., three-times size) heat exchanger 14than required merely for the condensation function. Because of thisrelatively large heat exchange size, the usual passive manners ofpreventing ice formation within heat exchanger 14 (e.g., those taught byAnderson U.S. Pat. No. 4,246,963 and Kinsell U.S. Pat. No. 4,352,273) donot produce fully acceptable results throughout the operating envelopeof the system of FIG. 1. At the same time overall system efficiency ismaintained by essentially always producing subfreezing outlet flow induct 88. Further, tendency toward icing in heat exchanger 14 is alsoincreased because of the close coupling of turbine 22 to plenum casing26 to reduce the length of duct 88 to minimize icing in the latter (andaccordingly minimize de-icing techniques for duct 88 itself).

It is to be understood that, as used herein, the description of the FIG.1 system as being one in which "all" fluid flow passes through filter91, refers to the FIG. 1 system in its filter-operating functional modeand the associated heating function for heat exchanger 14. Specifically,it is within the scope of the invention and the terms defined in thisparagraph, that a selective bypass of filter 91 may be included tomodulate the duty cycle thereof to increase its life. Such, of course,does not alter the capacity requirement of heat exchanger 14.

While heat exchanger 14 is discussed in greater detail below, one aspectof passive anti-icing control is accomplished by delivery of anotherwise waste-heat airflow through a passage 230 extending from theair cycle cooling machine 20 to a warming chamber 232 on casing 28. Tomore fully explain the source of the heating flow in passage 230, theconstruction and operation of the improved air cycle cooling machine 20will now be described in greater detail by reference to FIG. 2. Theturbine means 22 includes a hollow, generally cylindrical housing 98into which the turbine inlet duct 86 enters generally tangentially, andfrom which the turbine outlet portion 88 centrally extends in an axialdirection. Housing 98 comprises axially outer and inner portions 98a,98b and has defined therein a generally annular inlet passage 100 whichcircumscribes a bladed turbine wheel 102 and communicates with theturbine inlet 86. The compressor means 24 comprises a hollow, generallycylindrical housing 104 into which the inlet duct 76 axially enters andfrom which an outlet 106 generally tangentially extends to communicatewith the duct 78 of FIG. 1. Housing 104 has defined therein an annulardischarge passage 108 which circumscribes an annular diffuser section110 having formed therein an annular array of generally radiallyextending diffuser passages 112. Passages 112 extend between the inletand discharge passages 76, 108 and circumscribe the discharge end of abladed compressor impeller 114.

Shaft means 115, which extends between the mutually spaced turbine wheel102 and compressor impeller 114, include a main or inner shaft 116 whichextends at its left end through turbine wheel 102, and at its right endthrough the compressor impeller 114. The shaft means also includes afirst hollow outer shaft portion 118 fixedly connected to a secondhollow outer shaft portion 120. Shaft portion 118 coaxiallycircumscribes the inner shaft 116 and extends from portion 120 to aradially inner portion of an annular bearing runner plate 126 (having afunction subsequently described). Plate 126, as well as a right endportion of outer shaft portion 118, has extended therethrough an axiallyinner end portion 128 of turbine wheel 102, the plate 126 bearingagainst an annular shoulder 130 formed on impeller 102. Outer shaftportion 120 extends between portion 118 and an annular shoulder 134 onthe compressor impeller 114.

The turbine wheel 102, bearing plate 126, outer shaft portions 118, 120,and compressor 114 are frictionally locked together for conjointrotation by means of a pair of tightening nuts 136, 138 whichthreadingly engage the outer ends of the inner shaft 116 andrespectively bear against the outer ends of the turbine wheel 102 andthe compressor impeller 114. As these nuts are tightened, the turbinewheel 102 and compressor impeller 114 are forced inwardly along shaft116, in turn forcing the outer shaft portions 118, 120 into frictionalinterengagement. In this manner the shaft means 60 are frictionallylocked to the turbine, fan and compressor elements of the air cyclemachine 20.

Extending completely between the turbine housing 98 and the compressorhousing 104, and circumscribing the shaft means 60, is a hollow housing140. The housing 140 is secured to the turbine housing 98 by an annulararray of bolts 162 (only one of which is shown in FIG. 4) which extendssuccessively through annular flanges 164, 166, the turbine housing 98,and annular flanges 168, 170 on housing 140. At the opposite end of theair cycle machine 20 the compressor housing 104 is secured to housing140 by an annular array of bolts 172 which extend successively throughthe compressor housing 104, the diffuser 110 and into the housing 140.

This arrangement and joining method very advantageously permits theturbine inlet 86 and compressor outlet 106 to be "clocked" (i.e.,rotationally oriented) relative to each other in a wide variety ofmanners, thereby affording great installation flexibility to the coolingmachine 20.

A gas foil bearing system supports the shaft means 115 and iscontinuously lubricated by a portion of the airflow inlet passage 100used to rotationally drive the turbine 102 and compressor 114. Thebearing system comprises a gas foil thrust bearing 174 positionedbetween the turbine wheel 102 and the right end of outer shaft section118, a gas foil journal bearing 176 positioned at the right end of shaftsection 118, and a gas foil journal bearing 178 positioned at the leftend of outer shaft section 120. The gas foil bearings 174, 176 and 178are each generally similar in construction to those illustrated anddescribed in U.S. Pat. No. 3,615,121.

Foil bearing 174 comprises an annular inner thrust plate 180 which isdefined by a radially inner right end portion of housing 140 andcircumscribes the right end of outer shaft section 118. Plate 180 has arightwardly extending annular lip 182 which overlies a leftwardlyextending annular lip 184 on an annular outer thrust plate 186 thatcircumscribes a narrow neck portion 188 of the turbine wheel immediatelyto the right of shoulder 130. Plate 186 is positioned to the right ofplate 180, defining therewith an annular passage 190, and is securedaround its periphery to the housing 140 by an annular array of bolts192. Operatively positioned between the turbine wheel neck 188 and thethrust plate 186 is an annular knife-edged labyrinth seal 194. Theannular runner plate 126 extends in a radial direction partially intothe annular passage 190. Plate 126 is slightly thinner than thethickness of passage 190, thereby defining with plates 180 and 186 anannular clearance space 196 between plates 186 and 126, and an annularclearance space 198 between plates 126 and 180. Operatively positionedin each of the clearance spaces 196,198 is an annular array ofoverlapping foil elements (not shown) which function during operation ofthe gas foil thrust bearing 174 as described in the referenced U.S. Pat.No. 3,615,121.

Gas foil journal bearing 176 comprises a cylindrical bushing 200 whichcoaxially circumscribes a right end portion of the outer shaft section118 and is press-fitted into a circular bore 202 formed in the housing140. Interposed between housing 140 and shaft section 118 immediately tothe left of bushing 200 is an annular knife-edged labyrinth seal 204.The inner diameter of bushing 200 is slightly larger than the portion ofshaft section 118 which it circumscribes, and defines therewith anannular clearance space 206 which communicates at its right end with aradially inner annular portion of clearance space 198. Operativelypositioned within clearance space 206 is an annular array of overlappingfoil elements (not shown) which function during rotation of the shaftmeans 115 as described in the referenced patent.

Gas foil journal bearing 178 is similar in construction and operation tobearing 176 and comprises a bushing 208 press-fitted into a circularbore in housing 140, circumscribing a left end portion of outer shaftsection 120 and defining therewith an annular clearance space 212 inwhich is operatively positioned an annular array of foil elements (notshown). Interposed between housing 140 and shaft section 120 immediatelyto the right of bushing 208 is the annular knife-edged labyrinth seal104.

The gas foil bearing system (i.e., bearings 174, 176 and 178) islubricated, and provided with the necessary hydrodynamic supportingforce, by the use of bleed air from passage 100 in the following manner.A small portion of the pressurized bleed air entering the turbinehousing inlet passage 100 is forced, via a small transfer tube 216, intoan annular passage 218 which is defined between the turbine housing andfan housing sections 98b, 140 and circumscribes the flange lip 182. Thebalance of the bleed air entering inlet passage 100 is forced radiallyinwardly through turbine nozzle openings 219 and through the bladedportion of turbine wheel 102, becoming the cooling air upon its exitfrom the wheel to duct 88. From passage 218 bleed air is forced, via anannular series of bores 220 formed through the abutting flange lips 182,184, into a radially outer portion of the annular passage 190. Bleed airentering passage 190 is sequentially forced through thrust bearingclearance spaces 196, 198, through the journal bearing clearance space206 to the labyrinth seal 204.

Another portion of the bleed air entering the passage 218 is forced, viaa bore 222 in housing section 140 into on end of a transfer conduit 224which communicates at its opposite end with a small transfer passage226. Transfer passage 226 communicates with an annular passage 228which, in turn, communicates with the journal bearing clearance space212. Bleed air entering transfer passage 228 is sequentially forced intothe annular passage 228, through the clearance space 212 to thelabyrinth seal 204.

The airflow in clearance space 212 functioning with the gas foil bearingthereof experiences substantial heating prior to exhausting from thebearing and the housing 140 to passageway 230. This relatively hot,waste airflow is directed to the heat exchanger 14 as described abovewith respect to FIG. 1 for anti-icing purposes.

Returning now again to the heat exchange means 14, this heat exchangeris shown in greater detail in FIGS. 3-7. As best shown in FIG. 3, theexit duct 88 from the turbine 102 is very closely coupled to the inletplenum casing 26 of heat exchanger 14. A sealed connection between theadjacent ends of duct 88 and plenum casing 26 may be provided by asealing and closure element 89. The hollowed heated header bars areschematically illustrated in FIG. 3 by the dashed lines 234, and theseheader bars, supplied by heated air from duct 92, are disposed adjacentthe front face 236 of the heat exchanger core itself. The counterflowcore of the heat exchanger is depicted by dashed lines in FIG. 3 withthe flow from inlet plenum casing 26 passing from left to right in FIG.3 to exit through plenum casing 28. The heated airflow from plenumcasing 30 passes downwardly, with respect to FIG. 3, into the heatexchanger core to be turned in the triangular section 238 to then flowin direct counterflow relation to the other cool flow in the rectangularsection 240, before then again being turned downwardly in the triangularsection 242 to exhaust through the plenum casing 32. As such, theinternal core configuration of the counterflow heat exchanger 14 is ofconventional construction well-known to those skilled in the art. Thesetriangular and rectangular sections 238, 240, and 242 are depicted bythe associated dashed lines more completely in FIG. 5. The generaldirection of the cool flow passing from plenum 26 to plenum 28 is notedby the solid arrows in FIG. 5, while the relatively warm counterflowingair passing from plenum 30 to plenum 32 is depicted by the dashed arrowsin FIG. 5 for clarity.

As can be most clearly seen with respect to FIGS. 3 and 7, the relativeclose-coupling of the turbine 102 to the front face 236 of the heatexchange core has been found to cause a significant distribution ofairflow velocities across the inlet face 236. As depicted by the conicaldashed lines 244 in FIG. 3 and their associated circular projection asdepicted in FIG. 7, a circular central portion of the face 236 receivesthe cold airflow from turbine 102 at highest velocities. Effectively theairflow in plenum casing 26 would be distributed somewhat in a Gaussianstatistical distributional pattern across the face of inlet 236 withrespect to the velocity thereof. In other words, the exhaust plume ofairflow from turbine 120 produces a central area depicted by dashedlines 244 of high airflow velocity. More particularly, thecharacteristics of diffusion of the turbine exhaust would be similar toentrainment of a jet discharge into a plenum, where velocity and flowdiffuses into the volume in the profile of Gaussian distribution curve.Accordingly the zone within the circular dashed lines 244 represent thebulk of the inlet flow (or the center of the Gaussian curve) and thehighest velocity of airflow. Such distribution of the airflow presumessubstantially zero or very low flow restriction through heat exchanger14 with respect to the cold subfreezing airflow passing from plenum 26to plenum 28. As a result, this same stratification of airflow wouldextend through the heater core.

It is quite clear therefore, by observation of FIG. 7, that a smallercircle 244 would result in less heat transfer, since a larger portion ofthe heat exchange core would be relatively starved of airflow.Conversely, a larger circle 244 would result in greater heat transfer asmore and more airflow is spread across a greater percentage of the core.This distributional stratification, i.e. the circular pattern 244 isdirectly related, of course, to turbine exit velocity.

Turbine exit velocity can vary significantly throughout the duty cycleof the entire environmental control system. Testing has shown that whenthe turbine 102 is close-coupled to the heat exchanger 14, that changesin turbine exit velocity airflow produce significant changes in the flowand temperature stratification at the inlet face 236. Thisstratification produces significant deviations from expected predictionsof metal temperatures. Specifically, the concentration of relativelycold air from the turbine exhaust within the zone bounded by dashedlines 244 results in lower than predicted metal temperatures at theselocations. This therefore may create ice formation where otherwise icewould not be predicted. Additionally, the amount of heat transferbetween the two counterflowing airflows varies significantly frompredictions wherein such stratification exists. Typically this has beenaddressed in the prior art by a substantial increase or oversizing ofthe heat exchanger 14 to meet both water removal and heatingrequirements. Additionally, the predictability of the heat exchanger 14performance at off- design conditions is extremely problematic whereturbine exit velocities vary and are stratified as discussed above.

Accordingly, an important aspect of the present invention is theminimization of stratification of turbine velocities at inlet face 236to avoid excessive ice formation. At the same time, since the turbinedischarge flow rate may vary substantially in the FIG. 1 system toaccommodate the various modes of operation thereof, the invention allowsoperation of the system by reducing ice formation in varying conditionsof turbine discharge flow velocities. That is, as used herein,minimization of the flow velocity stratification encompasses actualreduction thereof, and/or increased variations in permitted turbinedischarge velocities. One manner in which the present inventioncontemplates such a result is the inclusion of a backpressure plate 246,shown in FIGS. 4-6, disposed within the outlet plenum casing 28. Moreparticularly, backpressure plate 28 is a relatively thin, rigid, flatmetal plate secured adjacent to, but spaced slightly away from the backside face 248 of the heat exchange core. Backpressure plate 246 isoffset a sufficient distance from face 248 to allow substantiallyunobstructed flow through all of the heat exchange core passages. Asillustrated, it may be straightforwardly rigidly secured to back face248 through securing elements 250.

The design, configuration and location of backpressure plate 246 is suchthat the overall pressure loss of the airflow passing from plenum casing26 to plenum casing 28 is higher than would be experienced in theabsence of plate 246, thereby allowing an increase in retention of thehot and cold airflows in heat transfer relationship inside the core ofthe heat exchanger, as well as increasing the retention time of the coldsubfreezing air adjacent the hot header passages 234. Placement of plate246 on the back side of the heat exchanger core assures that the airflowimpacting the inside surface 252 of plate 246 has experiencedsubstantial warming so that plate 246 itself will not tend to collectice. Inclusion of backpressure plate 246 covering a substantial portionof the rear face 248 has been observed to produce an improved airflowdistribution (i.e., reduction of the stratification as depicted by thedashed circle 244) so that more correct predictions of heat transferperformance and metal temperatures within the interior core of the heatexchanger 14 can be predicted. Three factors considered togetherdetermine the amount of blockage required (that is the size required ofbackpressure plate 246) to accomplish the desired goals of increasedairflow retention time and reduced flow velocity stratification acrossthe front face thereof. Specifically, these three factors include thedistance between turbine 102 and core face 236, the pressure dropexperienced across the core of the airflow passing from face 236 to face248, and the turbine exit velocity. It is believed plate 254 would beeffective in other specific systems if it covered at least 30 percent offace 248, or between about 30 percent and 80 percent of that face.

In a particular system, for example, backpressure plate 246 coveringapproximately sixty percent of the face 248 has resulted in sufficientblockage of the airflow to reduce the velocity stratification acrossface 236 to avoid localized initiation of icing thereon, improved heatexchange flow, and resulting overall acceptable operation of the systemof FIG. 1. In that particular instance, the spacing between surfaces 248and 252 was approximately five percent of the overall length of the heatexchange core extending from surface 236 to 248. As will be apparent tothose skilled in the art, spacing between faces 248 and 252 is importantto consideration of efficiency of the overall system sends a majorcomponent of pressure loss of the exiting airflow is in the turning lossof the air after it exits surface 248 and flows around plate 246, alongwith a second turning loss as this airflow rejoins the air exitingplenum casing 28.

The present invention further contemplates a modification and adaptationof the heat exchange apparatus as disclosed in Kinsell et al U.S. Pat.No. 4,352,273 entitled "Fluid Conditioning Apparatus And System". Moreparticularly, the Kinsell et al patent discloses a heat exchanger havinga bypass passage integrally constructed to be contained within the sameheat exchange enclosure as the heater core carrying the primary flow.Such bypass duct of the Kinsell et al arrangement was found todramatically improve the overall efficiency of the heat exchangearrangement by allowing lower subfreezing temperatures at the outlet forpurposes of cooling, while at the same time anti-icing conditions werealso improved inasmuch as the tendency toward icing in the primarypassage increased the pressure drop therethrough to permit more airthrough the bypass. This therefore reduced the cold air traversing theheat exchange core while the same amount of warm air in thecounterflowing passage ways was available. This increased thetemperature of the primary airflow thereby reducing tendency towardsinitiation of icing. To the extent necessary reference may be made tothe Kinsell et al patent for a more clear understanding thereof, and tothe extent required the Kinsell et al patent is incorporated herein byreference.

The arrangement disclosed in the Kinsell et al patent is not directlyapplicable to the arrangement illustrated in FIGS. 1-7 because theturbine exit velocities may vary significantly when passing through itsduty cycle of providing either cooling or heating exhaust airflowthrough outlet 13. In particular, during operational conditions of theenvironmental control system illustrated in FIG. 1 wherein there existsthe greatest variation in turbine exit velocity from the standard designcondition for heat exchanger 14, the percentage of bypass flow as wouldbe introduced by the Kinsell et al concept, is most critical. Thiscondition occurs during altitude heating condition when fan 70 isunloaded by ram air pressure in duct 54 and the lower density of airflow therethrough due to altitude, all combined with the fact that thebackpressure on turbine 102 is also lowest at the same time. This isparticularly true with respect to partially pressurized or unpressurizedaircraft. In these conditions the air cycle machine 20 still operates atits highest normal speeds and therefore produces the highest turbineexit velocities.

The present invention solves these problems by structure to minimizevariation in the bypass ratio of airflow passing from plenum casing 26to plenum casing 28, while still retaining the anti-icing benefits asdisclosed in the Kinsell et al patent. More particularly, this aspect ofthe present invention is accomplished by including a gap or bypass duct254 in the core of heat exchanger 14 equivalent in function andoperation to the gap or bypass duct disclosed in the Kinsell et alpatent. Gap 254 is disposed at one extreme side of the heat exchangercore instead of being located generally in the center of the heatexchanger core as disclosed in the Kinsell et al patent. In this mannerthe present invention recognizes that the bypass duct or gap 254, inorder to perform consistently in conditions of turbine inlet velocitystratifications caused by the close coupling of turbine 102 to inletface 236, must be located so that the bypass duct is preferably outsidethe location of high velocity flow as experienced within the areacircumscribed by the dashed line circle 244 in FIG. 7. By placement ofbypass duct 254 to the extreme side of inlet face 236, the airflowvelocity at this side location does not vary substantially even thoughturbine exhaust velocities may be varying dramatically. As a result theratio of bypass flow passing through bypass duct 254, in comparison tothe remainder of airflow passing through the heat exchange core in heatexchange relationship with the warming airflow, can remain predictable.

At the same time, to avoid freezing and additional icing conditions, asmall one pass counterflow heat exchange passage 256 is containedbetween the bypass duct 54 and the outside sidewall 258 of the entireheat exchanger 14. The one pass passage 256 carries counterflowing warmair flow which is passing from plenum casing 30 to plenum casing 32,rather than carrying the cool flow passing from plenum casing 26 towardsplenum casing 28.

Additionally, placement of bypass duct 254 immediately adjacent onesidewall of the heat exchange core and in non-alignment with the centralinlet of the turbine airflow passing into inlet plenum 26, has beenfound to provide additional benefits. Specifically, high velocity iceparticles which are normally entrained in the turbine exit velocityairflow will not normally reach the bypass duct 254. Such ice particlesbeing more dense than the air carrying them, will tend to pass throughthe center portion of the heater core and will stay away from the bypassduct 254. This avoids tendency towards icing across bypass duct 254which can bridge the gap thereof once ice tends to start accumulatingwithin bypass duct 254.

In addition to improved predictability of heat exchanger operationbecause of the relative constancy of the bypass ratio because theairflow entering bypass duct 254 is far more predictable because it isoutside the high velocity area 244, this aspect further improves theoperation of the FIG. 1 arrangement by permitting a smaller size heatexchanger core in heat exchange means 14 due to the reduced bypass ratiopermitted thereby. Specifically, with utilization of the side bypasspassage 254, as turbine exit velocity increases, this effectivelyreduces the bypass ratio to actually improve the heating capabilitythereof. Accordingly, this aspect of the invention takes advantage ofthe fact that in the heating mode there is a higher turbine exitvelocity (therefore more extreme velocity stratification) which is thesituation in which the reduced bypass ratio for improved heating isdesired.

Further modifications and adaptations to the internal bypass duct 254have been discovered to improve the operational characteristics thereofsuch that the heat exchanger 14 may function not only as a condenser butalso as a heating element, i.e. sufficiently sized to impart significantheat transfer to the exhaust flow through duct 13. More particularly,with respect to FIGS. 4-8, the bypass duct 254, in order to workproperly, must be wide enough such that ice will not tend to initiateaccumulation thereon. That is, the width of bypass duct 254 must bemaintained sufficiently wide so as to prevent accumulation of ice thatwould eventually bridge the width thereof to close the bypass duct. Onthe other hand, the size of the bypass duct 254 directly relates to theheat transfer characteristics of heat exchanger 14. In other words, ifthe bypass duct 254 is too large, adequate heat transfer forcondensation and water removal and other purposes will not be availableshort of a very significant increase in size and weight of the overallheat exchanger 14.

To therefore control and minimize the size of heat exchanger 14, thepresent invention contemplates inclusion of a closure plate 260 securedto the backside of gap 254 (i.e., in alignment with the plane of theexit face 248). Closure plate 260 is rigidly, sealingly, secured to theadjacent sidewalls of the bypass duct 254 so that the exhaustcross-sectional area of duct 254 is substantially reduced. In thismanner, the bypass ratio may be reduced substantially, in comparison tothe bypass ratio in the absence of closure plate 260, because of thereduced exit flow area thereof, thereby allowing lower rate of bypassflow through bypass duct 254 for a given turbine inlet velocity. Thus,while effectively reducing the bypass flow ratio, the width of passage254 has, very importantly, not been reduced. In this manner, the bypasspressure ratio may be made smaller for a given size and configuration ofheat exchanger 14 without increasing the possibility of ice accumulationwithin the bypass gap. For purposes of definition herein, therectangular gap 254 is referred to as having a length direction runningfrom face 236 to face 248, a height direction extending vertically inFIGS. 4, 6 and 7, and a width direction extending horizontally in FIGS.4, 6 and 7.

Also, it has been found to be important that the closure plate 260 bedisposed at the rear end of bypass duct 254 rather than more nearlyadjacent the inlet face 236. More specifically, at this rearwardlocation closure plate 260 creates a static pressure region 262immediately in front of plate 260 relative to airflow therethrough. Asbest depicted in FIG. 8, the bypass air is effectively "pushed around"the static pressure area 262 as shown by the arrows in FIG. 8. In doingso, the very cold bypass air, which may well contain ice particles,avoids impingement directly upon the exposed surface of plate 260 athigh velocity. By avoiding impingement of ice particles at high velocityon the plate 260, accumulation of ice thereon is avoided. In otherwords, by avoiding or reducing impingement of the airflow directly uponsurface 260, ice is prevented from forming thereon even though plate 260is not directly warmed by any heating source.

In this manner, by carefully selecting the length of the closure plate260, the bypass ratio may be selected to be substantially less thanwould be created by a gap 254 of equal width but without the closureplate 260. This dramatically improves the design flexibility for a givensize heat exchanger 14. It is believed closure plate 260 can beeffective through various lengths thereof from about 30 percent to 70percent or more of the height of passage 254.

It will be apparent from the foregoing that the very cold bypass airflowpassing through bypass duct 254 and exiting out the smaller portionopening thereof at face 248 will promptly come into contact with thealigned end face portion of plenum casing 28 and impinge directlythereon. As noted, such high velocity impingement of very cold air with,perhaps, entrained ice particles is strongly conducive to ice formationon the aligned portion of plenum casing 28. At the same time, designconfiguration constraints as well as minimization of pressure loss inthe airflow dictates that the aligned portion of the plenum casing 28cannot be remotely disposed from the opening of bypass duct 254.Accordingly, in the present invention the heating manifold 232 isdisposed on the exterior surface of plenum casing 28 in alignment withthe opening portion of bypass duct 254. The air exhausted from the airbearing system in the air cycle machine 20 is ducted through passage 230into manifold 232 to create warming on the exterior surface of plenumcasing 28 at this point of relatively cold, spot cooling by the bypassflow. In this manner the parasitic flow loss of the air bearing flow isutilized for "spot" warming of a cold location on the plenum casing 28.In this manner initiation of ice formation at this critical point on theinterior of plenum casing 28 is avoided. Normally, the amount of airused for air bearing cooling is between 2-5 percent of the systemairflow, and is adequate for maintaining the metal temperature at thecold spot location on plenum casing 28 above freezing. Air manifold 232may be readily attached as by welding or mechanical attachment means atthe desired cold spot location. Importantly the air manifold 232 hasexit openings 233 so as to promote continuous flow of air through theair bearing system.

It will be apparent to those skilled in the art that the closure plate260 may be utilized in a bypass duct which is located other than at theextreme side as illustrated in the preferred embodiment. That is, theclosure plate 260 may be utilized for the same purpose and function in acentrally located bypass duct as illustrated in the Kinsell et al U.S.Pat. No. 4,352,273. In such instance, the anti-icing features of airbearing exhaust manifold 232 may be equally utilized by moving thechamber 232 into alignment with the bypass duct, wherever it may be.

Various modifications to the specific embodiments illustrated will beapparent to those skilled in the art. Accordingly, the foregoingdetailed description should not be considered as limiting to the scopeand spirit of the invention as set forth in the appended claims.

Having described the invention with sufficient clarity that thoseskilled in the art may make and use it, what is claimed is:
 1. A systemfor conditioning a working fluid to be distributed from a source thereofto a point of use, comprising:an air cycle machine including acompressor mechanically driven by a turbine, said compressor receivingworking fluid from said source and operable to compress and heat theworking fluid, said turbine operable to expand and cool the workingfluid to subfreezing conditions prior to its delivery to the point ofuse; first means for receiving and cooling the working fluid dischargedfrom said compressor; reheater means for receiving and further coolingthe working fluid discharged from said first means; condenser heatexchange means, receiving working fluid discharged from said reheatermeans, for condensing vapor entrained in the working fluid, saidcondenser means receiving the subfreezing working fluid discharged fromsaid turbine to effect said condensing; separator means, receiving theworking fluid and condensed vapor discharged from said condenser means,for separating and removing the condensed vapor from the working fluid,at least a portion of the working fluid discharged from said separatormeans being directed through said reheater means to effect said furthercooling of the working fluid discharged from said first means, andsubstantially all of the working fluid discharged from the separatormeans being delivered to said turbine; a filter for removingcontaminants from the working fluid discharged from said separator meansprior to delivery to said turbine; said condenser heat exchange meansdefining a core having first and second passageways arranged for heatexchange between the fluids therein, said first and second passagewaysbeing configured and sized to heat the subfreezing working fluiddischarged from said turbine to a temperature desired for delivery tothe point of use, whereby all working fluid delivered to the point ofuse passes through said filter, said condenser heat exchange meansincluding:first inlet and outlet plenum chambers at opposite inlet andoutlet faces of said core, said first inlet and outlet plenum chamberscommunicating with said first passageway, said first inlet plenumchamber receiving the subfreezing working fluid discharged from saidturbine and being sufficiently close-coupled to said turbine to producea substantial stratification of flow velocity of the subfreezing workingfluid impinging upon said inlet face of the core, said first outletplenum chamber receiving and collecting the working fluid dischargedfrom the first passageway for delivery thereof to the point of use;second inlet and outlet plenum chambers communicating with said secondpassageway, said second inlet plenum chamber receiving the working fluiddischarged from said reheater means, and said second outlet plenumchamber receiving and collecting the working fluid discharged from saidsecond passageway for delivery thereof to said separator means; and flowredistributing means disposed in said first outlet plenum chamber forminimizing said stratification of flow velocities at said inlet face ofthe core.
 2. A system as set forth in claim 1, wherein said flowredistributing means comprises a back pressure barrier disposed closelyadjacent to, but spaced from said outlet face.
 3. A system as set forthin claim 2, wherein said barrier covers at least 30 percent of saidoutlet face.
 4. A system as set forth in claim 3, wherein said barriercovers between 30 percent and 80 percent of said outlet face.
 5. Asystem as set forth in claim 4, wherein said barrier covers about 60percent of said outlet face.
 6. A system as set forth in claim 2,wherein said barrier comprises a thin, solid plate affixed to said coreand spaced slightly from said outlet face.
 7. A system as set forth inclaim 6, wherein said plate is aligned with that portion of the inletface wherein the highest flow velocities of said subfreezing fluid flowis concentrated.
 8. A system as set forth in claim 7, wherein saidportion of the inlet face is the center portion thereof.
 9. A system asset forth in claim 1, wherein said condenser heat exchange means furtherincludes a bypass passage contained within the confines of saidcondenser heat exchange means and extending from said inlet face to saidoutlet face in parallel flow relatively to said first passageway, saidbypass passage located at said inlet face to be exposed only to relativelow flow velocities of said stratified velocities of subfreezing workingfluid impinging thereon.
 10. A system as set forth in claim 9, whereinsaid bypass passage is disposed at an extreme side of said inlet face,said second passageway including subpassages on both sides of saidbypass passage.
 11. A system as set forth in claim 10, wherein saidbypass passage is of generally rectangular configuration in the planesof said inlet face and said outlet face with a width substantially lessthan its height, said rectangular bypass passage having a lengthextending from said inlet face to said outlet face.
 12. A system as setforth in claim 11, further including a closure plate sealingly affixedwithin said bypass passage at a location adjacent said outlet face, saidclosure face extending completely across the width of said bypasspassage, and extending a preselected distance along the height of saidbypass passage.
 13. A system as set forth in claim 12, wherein saidpreselected distance corresponds to a desired ratio of fluid flowthrough said bypass passage to fluid flow through said first passageway.14. A system as set forth in claim 12, wherein said preselected distanceis between 30 percent and 70 percent of the full height of said bypasspassage.
 15. A system as set forth in claim 9, wherein said air cyclemachine includes a foil journal air bearing and a waste flow exhaustpassage for carrying heated, exhaust airflow from said foil bearing,said first outlet plenum chamber having a heating manifold carried on anexternal surface thereof in general alignment with fluid flow exitingsaid bypass passage, said heating manifold receiving heating airflowfrom said waste flow exhaust passage.
 16. A system as set forth in claim12, wherein said air cycle machine includes a foil journal air bearingand a waste flow exhaust passage for carrying heated, exhaust airflowfrom said foil bearing, said first outlet plenum chamber having aheating manifold carried on an external surface thereof in generalalignment with fluid flow exiting said bypass passage, said heatingmanifold receiving heating airflow from said waste flow exhaust passage.17. A system for conditioning a working fluid to be distributed from asource thereof to a point of use, comprising:an air cycle machineincluding a compressor mechanically driven by a turbine, said compressorreceiving working fluid from said source and operable to compress andheat the working fluid, said turbine operable to expand and cool theworking fluid to subfreezing conditions prior to its delivery to thepoint of use; first means for receiving and cooling the working fluiddischarged from said compressor; reheater means for receiving andfurther cooling the working fluid discharged from said first means;condenser heat exchange means, receiving working fluid discharged fromsaid reheater means, for condensing vapor entrained in the workingfluid, said condenser means receiving the subfreezing working fluiddischarged from said turbine to effect said condensing; separator means,receiving the working fluid and condensed vapor discharged from saidcondenser means, for separating and removing the condensed vapor fromthe working fluid, at least a portion of the working fluid dischargedfrom said separator means being directed through said reheater means toeffect said further cooling of the working fluid discharged from saidfirst means, and substantially all of the working fluid discharged fromthe separator means being delivered to said turbine; a filter forremoving contaminants from the working fluid discharged from saidseparator means prior to delivery to said turbine; said condenser heatexchange means defining a core having first and second passagewaysarranged for heat exchange between the fluids therein, said first andsecond passageways being configured and sized to heat the subfreezingworking fluid discharged from said turbine to a temperature desired fordelivery to the point of use, whereby all working fluid delivered to thepoint of use passes through said filter, said condenser heat exchangemeans including:first inlet and outlet plenum chambers at opposite inletand outlet faces of said core, said first inlet and outlet plenumchambers communicating with said first passageway, said first inletplenum chamber receiving the subfreezing working fluid discharged fromsaid turbine and being sufficiently close-coupled to said turbine toproduce a substantial stratification of flow velocity of the subfreezingworking fluid impinging upon said inlet face of the core, said firstoutlet plenum chamber receiving and collecting the working fluiddischarged from the first passageway for delivery thereof to the pointof use; second inlet and outlet plenum chambers communicating with saidsecond passageway, said second inlet plenum chamber receiving theworking fluid discharged from said reheater means, and said secondoutlet plenum chamber receiving and collecting the working fluiddischarged from said second passageway for delivery thereof to saidseparator means; and a bypass passage contained within the confines ofsaid condenser heat exchange means and extending from said inlet face tosaid outlet face in parallel flow relationship to said first passageway,said bypass passage located at said inlet face to be exposed only torelative low flow velocities of said stratified velocities ofsubfreezing working fluid impinging thereon.
 18. A system as set forthin claim 17, wherein said bypass passage is disposed at an extreme sideof said inlet face, said second passageway including subpassages on bothsides of said bypass passage.
 19. A system as set forth in claim 18,wherein said bypass passage is of generally rectangular configuration inthe planes of said inlet face and said outlet face with a widthsubstantially less than its height, said rectangular bypass passagehaving a length extending from said inlet face to said outlet face. 20.A system as set forth in claim 19, further including a closure platesealingly affixed within said bypass passage at a location adjacent saidoutlet face, said closure face extending completely across the width ofsaid bypass passage, and extending a preselected distance along theheight of said bypass passage.
 21. A system as set forth in claim 20,wherein said preselected distance corresponds to a desired ratio offluid flow through said bypass passage to fluid flow through said firstpassageway.
 22. A system as set forth in claim 21, wherein said aircycle machine includes a foil journal air bearing and a waste flowexhaust passage for carrying heated, exhaust airflow from said foilbearing, said first outlet plenum chamber having a heating manifoldcarried on an external surface thereof in general alignment with fluidflow exiting said bypass passage, said heating manifold receivingheating airflow from said waste flow exhaust passage.
 23. A heatexchanger for conditioning a working fluid, comprising:a heat exchangecore having first and second passageways for heat exchange between thefluid carried therein; first inlet and outlet plenum chambers atopposite inlet and outlet faces of said core, said first inlet andoutlet plenum chambers communicating with said first passageway, saidfirst inlet plenum chamber receiving working fluid in a subfreezingcondition and arranged such that the subfreezing working fluid impingeson said inlet face of the core with substantially varying flowvelocities across said inlet face, the highest flow velocities beingconcentrated in a centered position of said inlet face, said firstoutlet plenum chamber receiving and collecting the working fluiddischarged from said first passageway through said outlet face fordelivery to a point of use external to said heat exchanger; second inletand outlet plenum chambers communicating with said second passageway forcarrying relatively warm working fluid flow through the heat exchangecore in heat exchange relationship with colder fluid flow in said firstpassageway; a bypass passage defined within the confines of said coreand extending from said inlet face to said outlet face for carryingworking fluid from said first inlet plenum chamber to said first outletplenum chamber in parallel, bypassing relationship to said firstpassageway; and a closure plate sealingly affixed within said bypasspassage at a location adjacent said outlet face to extend partiallyacross said bypass passage in a direction reducing bypass flowtherethrough without reducing the minimum dimension of said bypasspassage.
 24. A heat exchanger as set forth in claim 23, wherein saidbypass passage is of generally rectangular configuration in the planesof said inlet face and said outlet face with a width substantially lessthan its height, said rectangular bypass passage having a lengthextending from said inlet face to said outlet face.
 25. A heat exchangeras set forth in claim 24, wherein said closure face extends completelyacross the width of said bypass passage, and extends a preselecteddistance along the height of said bypass passage.
 26. A heat exchangeras set forth in claim 25, wherein said preselected distance correspondsto a desired ratio of fluid flow through said bypass passage to fluidflow through said first passageway.
 27. A heat exchanger as set forth inclaim 23, wherein said bypass passage is disposed at an extreme side ofsaid inlet face, said second passageway including subpassages on bothsides of said bypass passage.